Isolation and characterization of a glycoprotein secreted by aortic endothelial cells in culture. Apparent identity with platelet thrombospondin.

A high molecular weight glycoprotein, reported to be secreted by endothelial cells (Sage, H., Crouch, E., and Bornstein, P. (1979) Biochemistry 18, 5433-5442), has been purified to apparent homogeneity from culture medium of adult bovine aortic endothelial cells. Purification was achieved by ammonium sulfate fractionation and successive chromatography on gelatin-Sepharose, Sephacryl S-300, and hydroxylapatite. The glycoprotein was found to be a disulfide-linked oligomer with a subunit molecular weight of 190,000, as judged by its mobility on sodium dodecyl sulfate (NaDodSO4)-polyacrylamide gels. The endothelial cell-derived protein is distinct from high molecular weight serum glycoproteins such as fibronectin and alpha 2-macroglobulin. However, immunological and structural studies indicate that the Mr = 190,000 glycoprotein is either identical with or closely related to thrombospondin, a glycoprotein contained in platelet granules and released in response to thrombin-induced aggregation.